Hematocrit is a blood test that measures the percentage of the volume of whole blood that is made up of red blood cells. This measurement depends on the number of red blood cells and the size of red blood cells. The hematocrit (Ht or HcT, British English spelling hematocrit) also is known as packed cell volume (PCV) or erythrocyte volume fraction (EVF). It is normally about 45% for men and 40% for women. As part of detecting many types of blood analytes, a colorimetric testing system is used. In such a test, after isolating the analytes to be measured and reacting the analytes to produce a color change, the reflectance or some other optical measurement is taken. The optical measurement is proportional to the amount of analyte in the sample. In many such calculation schemes, red blood cells are separated from the sample before measurement. This is because the red blood cells affect the color of the color change resulting from the reaction of analytes. The separation of the red blood cells typically is performed using a red blood cell separation layer in the strip, which layer may, for example, be made of a glass fiber matrix. The red blood cells are removed because they would otherwise interfere with the colorimetric test. However, it is difficult, if not impossible, for 100% of the red blood cells to be removed.
In many situations, the occurrence of red blood cells affects the colorimetric test. This negatively affects the accuracy of the test. Although a pre-calculated correction factor can be used in many cases, there are still effects from the red blood cells.
The measurement of low-density lipoprotein (LDL) cholesterol is an important health measurement in the determination of health, especially cardiovascular health. It is desirable to have fast on-site measuring systems for LDL that does not require a laboratory or other facilities. In this way, health professionals may speak with patients immediately after a sample is taken, instead of having to wait days for test results to come back from a lab. In this way, the patient's history and status will be fresh in their mind and, therefore, lead to better results and analysis of patient health.
In the case of the measurement of the concentration of a lipid, such as high density cholesterol (HDL), the test includes placing a drop of blood on a test strip and inserting the test strip in a meter that outputs the result of the test as an electronic signal. The lipid test generally includes a step in which red blood cells are separated from the plasma. The concentration of the lipid then is determined using a colorimetric test. Unfortunately, in many scenarios, the measured concentration may not be reflective of the actual concentration of the lipid (analyte) measured.